Conventional magnetic recording is generally considered to be limited to areal densities below about 1 Terabit/in2 where the bit dimension is around 20 to 25 nm. The fringing effect from the magnetic pole requires the pole width to be essentially dimensionless (zero width) in order to have the erasure width as small as the bit. This condition is certainly impossible to accomplish and thus assisted magnetic recording is needed to achieve a higher areal density. TAMR is expected to be one of the future generations of magnetic recording technologies that will enable recording at ˜1-10 Tb/in2 data densities. TAMR involves raising the temperature of a small region of the magnetic medium to above its Curie temperature where both of its coercivity and anisotropy are virtually eliminated so that magnetic writing becomes easier to achieve even with weak write fields characteristic of small write heads in high recording density schemes. The recording transition is written with the magnetic field generated by the magnetic pole and then the media is cooled down so the written signal is stored. Very quick thermal heating and cooling is required to limit the heat-affected zone so the adjacent track/bits will not suffer erasure. In TAMR, optical power from a light source, typically a laser diode (LD) mounted on the slider, is converted into localized heating in a recording medium. Thus, with a sharp temperature gradient of TAMR acting alone or in alignment with a high magnetic field gradient, data storage density can be further improved with respect to current state of the art recording technology.
In addition to the components of conventional write heads, a TAMR head also typically includes an optical waveguide (WG) and a plasmon generator (PG). The waveguide serves as an intermediate path to guide the external laser light to the PG where the light optical mode couples to the propagating plasmon mode of the PG. After the optical energy is transformed to plasmon energy with energy transmission along the PG, it is concentrated at the medium location where heating is desired. Ideally, the heating spot is correctly aligned with the magnetic field from the write head to realize optimum TAMR performance. However, the intense heat generated by the PG tends to cause performance degradation within a short period of time. Also, the high temperature along the PG surface during the write process creates a reliability problem with the PG material that is usually a noble metal such as Au or Ag. Failure analysis shows a PG shape change and a deep recession in one or more PG surfaces.
There is an urgent need to develop a methodology that can improve the thermal robustness of the PG. High temperature deposition has been attempted but presents a new issue since the entire deposition chamber is at an elevated temperature that exceeds the blocking temperature of IrMn or other anti-ferromagnetic materials in the AFM layer used to fix the pinned layer magnetization direction in the sensor element of the adjoining read head. Laser annealing provides more localized heating. However, optical reflection of laser light from many materials in the recording head can lead to other problems. Thus, a new concept of improving PG reliability is needed that does not degrade other components in the TAMR write head or in the adjoining read head.